@testset "200.number-of-islands.jl" begin
    @test lands_num([
        ["1","1","1","1","0"],
        ["1","1","0","1","0"],
        ["1","1","0","0","0"],
        ["0","0","0","0","0"]
      ]) == 1
    @test lands_num([
        ["1","1","0","0","0"],
        ["1","1","0","0","0"],
        ["0","0","1","0","0"],
        ["0","0","0","1","1"]
      ]) == 3
end
